I was going to comment on the metal box within the wooden one as a capacitance adder, but for an analog Theremin it's probably fine as absolute sensitivity isn't a primary concern. But the most sensitive part of any Theremin is exposed at the antennas, so I wonder how much shielding actually helps with interference and such? Best I think to have a large voltage swing at the antennas and thus swamp environmental interferers. Moog's earlier physical designs were likely strongly influenced by radio construction standards at the time (metal chassis, tubes & controls mounted on it, etc.) rather than best practices for solid state Theremin construction. That said, having the audio circuits shielded can't hurt. I wish you luck with this project!